In the polymerization of alpha-olefins, it is known to use catalyst systems comprising a transition metal compound and an organometallic compound. It is further known that the productivity of such catalysts can generally be improved if the transition metal compound is employed in conjunction with a metal halide such as magnesium halide. Some especially active catalyst components have been obtained by reacting an oxygen-containing organic compound of transition metals with a magnesium dihalide and then reacting that product with an organoaluminum halide.
The present invention is concerned with new high productivity catalysts which employ scandium, yttrium, or rare earth metal halides in place of at least part of the magnesium dihalide.